Category: Thesis

Author: HANNA SKLIAROVA ; Type of thesis: Master Thesis
Abstract: Continue reading →

Author: OLGA CHERENKOVA ; Type of thesis: Master Thesis
Abstract: A nuclear reactor is a system that contains and controls sustained nuclear chain reactions. Reactors are used for generating electricity, moving aircraft carriers and submarines, producing medical isotopes for imaging and cancer treatment, and for conducting research. Fuel, made up of heavy atoms that split when they absorb neutrons, is placed into the reactor vessel (basically a large tank) along with a small neutron source. The neutrons start a chain reaction where each atom that splits releases more neutrons that cause other atoms to split. Each time an atom splits, it releases large amounts of energy in the form of heat. The heat is carried out of the reactor by coolant, which is most commonly just plain water. The coolant heats up and goes off to a turbine to spin a generator or drive shaft. So basically, nuclear reactors are exotic heat sources.
Cyclotrons continue to be efficient accelerators for radio-isotope production. In recent years, developments in the accelerator technology have greatly increased the practical beam current in these machines while also improving the overall system reliability. These developments combined with the development of new isotopes for medicine and industry, and a retiring of older machines indicates a strong future for commercial cyclotrons. For both systems, efficient cooling is required. Nowadays liquid metals are in wide use for this purpose. Liquid metal cooled reactors were first adapted for nuclear submarine use but have also been extensively studied for power generation applications. Liquid metals have safety advantages because they have high heat transfer characteristics, due to high boiling point, no high vapor pressure, and they allow a much higher power density than traditional coolants. Cooling by liquid mercury, sodium, NaK, lead has been studied and used. But due to numerous imperfections of these coolants (such as toxicity, high vapor pressure, not appropriate melting/boiling points, corrosion etc) it is necessary to develop new cooling systems for research and industrial purposes. Thus after choosing the new coolants (liquid metals with desirable properties) for target cooling we will develop the protection coatings for tubes taking into account factors which influence corrosion such as solution pH, oxidizing agent, temperature, velocity, stresses, impurity content. So we can conclude that development of new protective thin films, coatings, claddings are required and mandatory for protection. For its development we propose to use the magnetron sputtering which is a very perspective method for obtaining of thin films. One feature of magnetron sputtering which explains its wide use for the coatings is the low charged particle fluxes reaching a substrate. By this method we can obtain coatings on conductive materials as wellas on nonconductive, also on materials with low melting points. Sputtered films typically have a better adhesion on the substrate than evaporated films. Thereby the producing of protective coatings from liquid metals coolants embrittlement used for nuclear reactors and target cooling in the radiopharmaceutical sphere has been under development within the bounds of this project. Continue reading →

Author: DANIEL ADRIEN FRANCO LESPINASSE ; Type of thesis: Master Thesis
Abstract: THIS THESIS IS PROTECTED BY TRADE SECRET. IF YOU WANT TO CONSULT IT, You need to contact the Master Director

In this research, an innovative source was built and were performed the preliminary tests to study a magnetron sputtering configuration in order to deposit quarter wave resonator cavities (QWRs) .This project is based on the deposition of niobium onto copper cavities that will be used for the development of an ion accelerator. To do this, it was required the development of the vacuum chamber using a rotating magnetron , a test cavity and a test cathode, both of them made with stainless steel. The methodology was established depositing stainless steel onto quartz substrates placed along the cavity in order to observe the uniformity of the coating. The results are focused on thickness measurements. In addition to the sample thickness measurements was realized the film stripping test in order to see differences in deposition rates, all over the resonator wall. Were studied three groups of test changing the configuration of the magnetic field and other parameters like sputtering pressure, power and also time of deposition. Finally was found that the vacuum system was successfully assembled and is available for thin film deposition. Preliminary deposition tests with SS were performed and different thicknesses were observed along the cavity. Thickness values are higher on the internal region of the cavity where the target is closer and lower thicknesses are in the top where might be holes in the magnetic field. Also, the appropriate pressure found to reduce differences in thickness along the cavity was 8×10-3 mbar and the stripping test shows that the deposition rates are different on the top of the cavity probably due to the absence of magnetic field. Nowadays, we are modifying the configuration of the magnetron in order to improve the plasma on the top of the cavity. Continue reading →

Author: ANDREA CAMACHO ; Type of thesis: Master Thesis
Abstract: This works deals with the A15 compound synthesis on niobium samples and over the internal surface of niobium cavities by means of induction heating. Specifically, three compounds were studied: Nb3Ga, Nb3Al and Nb-Al-Ga. As for the preparation of the niobium samples, they were treated with BCP solution in order to polish the surface. The niobium cavities were treated with centrifugal tumbling, BCP solution and high pressure water rising. Subsequent, the samples, or cavities, were placed into an inductor controlling the voltage, time, sample position, temperature, type and pressure of gas used. The highest critical temperature
obtained was 18 K and Tc 0,35 K, in Nb-Al-Ga#1 sample by inductive measurement. Mapping analysis showed the uniform diffusion of aluminum into the niobium, and the gallium diffuses creating channels into niobium. The composition was measured by EDS obtaining (82±1)% wt. Niobium, (11,3±0,9)% wt. Gallium, (4,7±0,2)% wt. Aluminum and (1,9±0,1)% wt. Oxygen. Finally, RF test confirmed that the cavities obtained after the annealing were normal conductive indicating that the preparation parameters must still be optimized. Continue reading →

Author: VLADA PASTUSHENKO ; Type of thesis: Master Thesis
Abstract: A solar collector is an apparatus that collects the sunlight energy, and then alters this energy into a more usable or storable energy form. The absorber surface used in thermal solar collectors requires high absorptance in the solar spectrum and low emittance. Several techniques, such as vacuum techniques, are currently used to produce solar absorber surfaces. However, the desired characteristics of the solar absorber coating may be better controlled by direct electrodeposition. Other electrodeposition advantages are basically rapidity, low cost, free from porosity and industrial applicability. Copper substrate was chosen due to its use in a large variety of domestic and industrial piping as a thermal and electrical conductor. Black chromium is an important coating material used in solar thermal systems as a spectrally selective surface. This coating is usually obtained by electrodeposition from sulphate free chromium (VI) aqueous solutions which represent a health and environmental hazard due to the presence of Cr (VI), a known toxic and carcinogenic agent. Recent developments in green chemistry have shown that ionic liquids can be used as electrolytes, allowing the deposition of a wide range of materials with negligible environmental and health impacts. Continue reading →

Author: Atroshchenko Konstantin ; Type of thesis: Master Thesis
Abstract: International Committee for Future Accelerators recommended that the Linear Collider design has to be based on the superconducting technology. And this is the reason why the international scientific society directed efforts to improving superconductive technology and reducing its cost.
In this work, in the framework of researching a valid alternative to Nb for RF superconducting cavities, thin film Nb3Sn has been investigated. The goal will be the achievement of superconducting cavities working better than the Nb ones at 4.2 K.
In order to improve the existing technology of substrates coating by thermally diffused Nb3Sn a new high temperature annealing technology has been developed. In the first part of the work, is given the short theoretical review of RF superconductivity, main superconductors that are used to be a good alternative to a pure Nb and fundamentals of the induction heating theory. Second part is dedicated to the existing double furnace technology, developed in the superconductivity lab in LNL. The influence of preliminary surface treatments like glow discharge of the sample, anodization and chemical etching on the quality of thermally diffused Nb3Sn was studied. And in the third part is given the description of the new induction heating system, suggested for annealing of the 6 GHz cavities. Also in the third part we will go through the results of coating samples and cavities with thermally diffused Nb3Sn with high temperature annealing and the results of the RF – test.
Finally, it is important to mention, that from the very beginning of investigation the induction heating for annealing 6 GHz cavities it became clear that the technology has an enormous potential in producing thermally diffused Nb3Sn. Continue reading →

Author: Chirkov Dmytro Vasiliovych ; Type of thesis: Master Thesis
Abstract: The main aim of this work is try to electrodeposit metallic niobium films from room-temperature ionic liquids.
Nowadays electrochemical surface treatment is one of the most used approaches in industry.
Aqueous solutions has been the most widely used process mainly because of advantages such us low cost, non-flammability, high solubility of electrolytes, high conductivities resulting in low ohmic losses, high solubility of metal salts and high rates of mass transfer. However, despite these advantages there are several limitations in using aqueous solutions such as limited potential windows, gas evolution processes that can result in hydrogen embrittlement, passivation of substrates, electrodes and deposits, and the necessity for hazardous complex agents such as cyanide, causing environmental contamination. These are the reasons why new non-aqueous solutions to electrodeposit niobium have been researched.
One of the main limitations in using aqueous solutions is their narrow electrochemical window. The major reason for carrying out electrodeposition in non-aqueous electrolytes (such as conventional organic solvents, molten salts or ionic liquids) is water and air stability and the wide electrochemical window of these media.
Alternatively, also high temperature molten salts have been used extensively for niobium electrodeposition. They have wide potential windows, high conductivities and high solubility for metal salts. In fact, they have most of the advantages of aqueous solutions and overcome most of the limitations of aqueous solutions, but their one major limitation is the very high temperature (more than 750°C).
Therefore, the alternative to high temperature molten salts was an ionic substance that melts at a low temperature. Over the last few decades, room temperature ionic liquids have been widely studied in various scientific fields due to their interesting properties, such as negligible vapour pressures, high chemical and thermal stability, acceptable intrinsic ionic conductivity and wide potential window.
Ionic liquids are molten salts with melting points below 100°C and they consist entirely of cations and anions. The development of ionic liquids, especially air and water stable types, has attracted extensive attention since they have outstanding physical properties.
The aim of this work will be the analysis of available literature data in order to have precise knowledge about niobium behavior in the different electrolytes and to get new information about possible electrolytes based on ionic liquids. Continue reading →

Author: Jahanfar Hanieh ; Type of thesis: Master Thesis
Abstract: 

The economic damages in the world because of corrosion are considered as one of the problems in economic developments . The global economic damages of corrosion is in the scale of billion dollars . Just in the US in one year the total economic damage because of corrosion is around a half of billion dollars ! .
As much as corrosion is dangerous and considerable, protection against corrosion is important which is seriously followed by researchers .
The word protective usually refers to the corrosion . The corrosion of metals typically takes place in the reinforced concrete. It happens when there is an anode where oxidation occurs, and a cathode where reduction occurs.
Considering the importance of protection against corrosion , my thesis project was started with one of the best methods of protection which is thin film deposition and with one of the most interesting protective material which is CeO2 .
Also its necessary to mention that another projects have been done in the superconductive laboratory of INFN in Legnaro with the object of deposition of CeO2 thin film as a protector but in the last project the used target has been CeO2 target and just a certain sputtering technique has been used so we decided to compare different sputtering techniques which was possible through using different power supplies and comparing them, with a more industrial target .This is why we chose Ce target and 4 different kinds of power supplies as DC, AC ,RF and Pulsed DC to be compared through using the main system which was reactive magnetron sputtering . By using the mentioned 4 power supplies and comparing them the most important parameters have been deposition rate and film stoichiometry as sensitive functions of reactive gas partial pressure .
Meanwhile as one of the examples of corrosion is oxidation of the copper coins we chose protection of coins as the main application for my thesis. Circulating mintage of copper coins (Like 1 , 2 or 5 cents) just in Italy have been around 400 million coins in 2009 . If we multiply this circulation to the cost of mintage new coins to be replaced with old ones which are usually effected by corrosion we can estimate a big economic damage in Italy because of corrosion So we decided to specifically apply our protection method to the Euro copper coins as a reasonable application. Continue reading →

Author: Li Jin Hai ; Type of thesis: Master Thesis
Abstract: The superconductor accelerator cavity is one of the most important and perspective technology for an advance accelerator. For example, the International Committee for Future Accelerators decided that the Linear Collider design had been based on the superconductor technology. Moreover, the accelerator operating with continue wave (CW) mode must use the superconductor technology in stead of the normal conductor technology, such as the Accelerator-driven sub-critical reactor system (ADS), the Accelerator Transmutation of Waste (ATW), the Accelerator Production of Tritium (APT), and so on.
In order to meet all kinds of application, the scientific world interest is now focus on further developments of new resonant cavities fabrication techniques to reduce cost and improve the performance of the accelerator cavity. To realize this object, one of the important methods is to pursue research on new materials. The goal will be the achievement of superconducting cavity working better the Nb ones at 4.2K. For example, the better parameters of the Tc, the surface resistance, the critical field Hc and the Q value are needed.
Up to now, the most possible candidate is Nb3Sn. The Nb3Sn has not only the better superconductivity parameters, but also the stable property and the easy fabrication. There are two methods to fabricate the superconductor cavity with the Nb3Sn, which are including the diffusion method and the multilayer deposition method. In the thesis, we focus on the multilayer deposition method, and …… Continue reading →